Process for the production of aromatic dicarboxylic acids



United States Patent i) assess? PROCESS FOR TEE PRODUCTIGN F AROMATIC DICARBOXYLIC ACIDS Josef Binapfl, Krefeld, Germany, assignor to Far-henfahriken Bayer Aktiengesellschaft, Leverlrusen, Germany, a corporation of Germany No Drawing. Application March 31, 1953 Serial No. 346,023

It is known to transform aromatic hydrocarbons with aliphatic side chains, especially toluene and xylene, into the corresponding carboxylic acids, by the action of oxygen-containing gases. The oxidation of such hydrocarbons succeeds even under mild conditions. Thus one can for example product benzoic acid by passing air through toluene, or phthalic acid or isoor terephthalic acid by passing air through 0-, mor p-xylene respectively, at temperatures below about 200 C. These reactions can be accelerated by the use of pressure and the addition of catalysts. It has already been proposed to react the hydrocarbons in organic solutions or in aqueous solutions or suspensions of bases or acid-binding salts or mixtures thereof, in which case catalysts may suitably be added. The dilution of the hydrocarbons has however the consequence that one must employ very energetic conditions, working for instance at 250 under a pressure of 60 atmospheres. The reaction does not then, however, lead simply to the corresponding carboxylic acids. Besides the acids there are also produced alcohols and aldehydes. The oxidation of a second alkyl group of the benzene nucleus is rendered especially diflicult, so that for example when using pxylene, only a little terephthalic acid results, in comparison with considerable quantities of p-toluic acid, as Well as aldehyde and unused xylene.

It is further known that the corresponding carboxylic acids may be obtined by heating halogen alkylated benzenes in the presence of aqueous alkalies, where by splitting-off of the halogen of the alkyl residue produces first the corresponding alcohol and by dehydrogenation of the latter, the carboxylic acid. The presence of oxygen in this reaction can lead in certain cases to the combination of the hydrogen evolved, to form water. If in this process besides a halogen-alkyl residue, there are available other alkyl residues, at the benzene nucleus, e. g., a methyl group, these are not affected. Thus there is produced for example from p-xylyl chloride by heating with caustic soda under pressure even in the presence of oxygen, not terephthalic acid but ptoluic acid or its salts.

It has now been surprisingly found that one can produce aromatic dicarboxylic acids in good yields, by heating halogeno-methyl-alkyl benzene in aqueous suspensions in the presence of bases and of oxygen or oxygen-containing gases, and preferably under high pressure, if one carries out the reaction in the presence of oxidation catalysts.

According to this process not only the halogeno-alkylgroup but, in contrast to the oxidation of dialkyl-benzenes with oxygen and the reaction of halogen alkylalkyl-benzenes with caustic alkalies in the presence of oxygen, also the alkyl groups are to a considerable degree transformed into carboxyl groups. The aforesaid process thus represents an important route for obtaining technically valuable phthalic acids, as the halogenomethyl-alkyl benzenes preferably serving as starting ma- 1C Patented Sept. 2, 1958 terials are easily obtained for instance by the action of formaldehyde and hydrochloric acid on toluene.

Among the halogeno-methyl-alkyl benzenes which ac cording to the foregoing process can with advantage most suitable be oxidised to the corresponding dicarboxylic acids are preferably: l-chloromethyl-4-methyl benzene and l-chloromethyl-Z-methyl benzene; further for instance l-chloromethyl-3-methyl benzene, l-bromomethyl-4-methyl benzene, l-bromomethyl-Z-methyl benzene, 1-bromomethyl-3-methyl benzene, l-chloromethyl- 4-ethyl benzene 1-chloromethyl-3-ethyl benzene, 1- chloromethyl-4-n-propyl benzene, l-chloromethyl-Z-npropyl benzene, 1-chloromethyl-3-n-propyl benzene, lchloromethyl-4-isopropyl benzene, l-chloromethyl-Z-isopropyl benzene, l-chloromethyl-3-isopropyl benzene, lbromomethyl-4-isopropyl benzene, 1-chloromethyl-4- amyl benzene, l-chloromethyl-Z-amyl benzene and l-chloromethyl-3-amyl benzene. mixtures of these materials, for example a mixture of l-chloromethyl-4-methyl benzene and l-chloromethyl-Z- methyl benzene, and then separate from one another the resulting phthalic and terephthalic acids.

Suitable oxydation-catalysts for the foregoing process are for instance oxides and/or heavy metal salts such as those of silver, cobalt, copper and manganese, or lead oxide or peroxide, or naphthenates or stearates of cobalt or manganese, or mixtures of such materials.

The process is advantageously so carried out that one brings the halogeno-methl-alkyl benzene and the catalyst into an aqueous caustic alkali such as sodium, potassium or calcium hydroxide solution, and introduces oxygen or air with thoroughmixing. The reaction can be accelerated by employing elevated temperatures and if necessary pressure. The temperature during the reaction may very according to the conditions. Good results were obtained with temperatures above C., the upper limit being given only by the decomposition temperatures of the reaction components and by the resistivity of the construction material. In general especially good results were obtained with temperatures ranging from about to about 250 C.

To achieve high reaction velocities it is advantageous to work under elevated pressure. It can also be arranged that oxygen or air is compressed into the mixture in a stirringor shaking-autoclave. Suitable pressures lie for instance between about 20 and about 250 atm. and especially between -250 atm. The carrying out of the process on a technical scale can also take a continuous form when one allows the reaction mixture to run through a pressure vessel into which oxygen or air is compressed.

The concentration of the alkali to be used can lie between wide limits, for example between about 1% and about 50% and especially between about 20 to about 33%. To achieve good yields it is advantageous to use at least such a quantity of basic material that all the acids released by the reaction i. e., the hydrogen halide and the organic acids, will be neutralized. Since besides the aromatic dicarboxylic acids there are also produced small quantities of other acid oxidation products such as oxalic acid or carbonic acid, it is recommended to use an excess of basic materials over the amount calculated for the production of hydrogen halide and aromatic dicarboxylic acids, so that the reaction mixture is in every case still alkaline at the end of the reaction.

The necessary reaction conditions appropriate to an individual case can easily be determined by simple experiment.

The following examples are given for the purpose of illustrating the invention.

In certain cases 0116 can USE 3 Example 1 141 g. (1 mol) of l-chloromethyl 4 methyl benzene are treated with air in the presence of 900 g. of 29% caustic soda solution, 1.5 g, lead ;oxide and 1.5 g. lead peroxide in an autoclave of acidfe'sistantfsteel, with stirring, at 250 C. andat a pressure of 170 to 250atm. In the mass, as the oxygen contentin the reaction vessel falls (end-content of oxygen in theexliaust gas, 2%+3%) the'residual gas is'allowedto escape and the pressure vessel is newly filled with fresh compressed air. 'After about '7 hours the oxygen contentbecomes gradually stationary. After acidifying the reaction procluct with dilute sulphuric acid'one obtainsi'a white..deposit which. consists of halogen-free terephthalic, acid. stilLcontaining; about 6%'-7 p-toluic acid. Theyieldfof purete'rephthalic acid' amounts to l23fg. ,1(=74% of'theory).

Example 2 1 A mixture of 77 g.v /2, mol-) of, l-chloromethylA- ethyl'benzene, produced bythe knownprocess-by thereaction of formaldehyde on; ethylbenaenein the.p resence of hydrochloric acid, 850 g. of. 20%,caustic soda solution, 3 g. of lead -oxide and 2 g'.;of lea d peroxide is treated by air at 265270. C. atiapressure of about 90 atm. in an autoclave ofacid resistant steel. In the; mass, as the oxygen contentiri the, reaction vessel falls (end content of oxygen in the exhaust, gas about. 3%: 4%) the residual gas is allowed to escape-yandthe pressure vessel is, newly filled. with freshcompressed air. After about 12 hours the oxygen .contcntbecomes gradually stationary. The reaction mass is thentreatedwith steam for about 4.hours. A- small ,quantitytabout 2 g.) of an oily distillate is separatedin this manner. In the vessel remain a clear alkaline solutionand about ll g. of a' resinous residue. 'Ifhesolution is separated andacidified with dilute sulphuric acid. One obta-ins 37 g. of terephthalic .acid, (=44% of-theory),

Example 3 g A mixture of76 parts byweight ofzlchloromethyllmethyl benzene and 65 parts -byweightof 1-.chloro-; methyI-Z-methyl benzene, such ;as isproduced by, known processes by the reaction offormaldehyde: on gtoluene .in the presence of hydrochloricgacid jsltreatedzwith under the conditions specifiedin Example-l, in the presence of 950 parts by weight of. 28%? caustic-.sodat. solution. product with dilute sulphuricacid one obtains a white? deposit, which after filtering and-repeated-:washingwith water consists of 59 parts by weight pf. terephthalicv acid- By acidification'of the grey, mealy. reaction From the filtrate and the-washing ;water 48: parts by.

weight of phthalie acid can be-recovered by extraction with ether. As a sideaproduct a small quantity of p-. toluic acid is produced. 3

I claim: ,7

1. A process for the production ofaiiomaticfldicarboxylic acids'which comprises heating,;an,; aqueous suspension of. a mono-halogenomethyl monorlower alkyl; benzene, said'lower alkyl substituent .containingtat. least one hydrogen substituent on-the benZene moietyTIinking. carbon atom and thehalogeno substituenta'being; see

lected from the group consisting of-chlorine and-bromine,v

in the presence of:a causticbase and oxygenandiaheavy. metal containing -oxidation -catalyst,; whereini the; heavy metal is. selected from-the group consisting: of. silver,. cobalt, copper, manganese. and leads:atrtemperaturesrang ing from about 100 Cato-about: 270"; 6-.

2. The process. ofclaim l-wherein,;.elevated; pressure: conditions are employed.

3. The process of claim '1 whereintairuisithe soyrce ofoxygen.v i V Y 4. A process for the production of phthalic acidt which 7 comprises heating at temperatures from aboutn2'65, to about 270 Cpa 1-halogenomethylg2 lower alkyl-j benw.

zene, said lower alkyl substituent containing at least one hydrogen substituent on the benzene-moiety-linking'carbon atom, in aqueous suspension in the presence of a caustic base and air and a heavy metal containing oxidation catalyst, wherein the heavymet'al is selected from the group consisting of silver, cobalt, copper, manganese and lead, under elevated pressure, the l-halogenosub stituent being selected from the group consisting of chlorine and bromine.

5. A process for the production of phthalic acid which comprises heating at temperatures from about to about 250 C. a 1-halogenomethyl-2-methyl benzene in aqueous suspension in the presence of a caustic base and air and a heavy metal containing oxidation catalyst, wherein the heavy metal is selected from the group consisting of silver, cobalt, copper, manganese and lead, under elevated pressure, the 'l-halogeno substituent being; selected from the group consisting of chlorine and bromine.

6. A process for the. production of terephthalic acid which comprises heating under elevated pressure attemperatures from about 150 C. to about 270 C. an aqueous suspension of a l-halogenomethyl-4-lower alkyl benzene, .said lower alkyl substituent containing at least one. hydrogen substituent on the benzene-moiety-linking carbon atom and the halogenosubstituent being selected from the group consisting of chlorine and bromine,;in the presence of a caustic base and oxygen and a heavy metal containing oxidation catalyst, wherein the heavy metal is selected from the group consisting of silver, cobalt, copper, manganese and lead. I

7. The process of claim 6 wherein the 4-lower alkyl substituent is methyl.

8. The process of claim 6 wherein the l-halogenomethy1-4-lower alkyl benzeneis l-chloromethyl-4-methyl benzene. W

9. A process for the production of terephthalic acid which comprises heating at temperatures from aboutr265 to about 270 C. an 1-halogenomethy1-4-ethylbenzene, in aqueous suspension in the presence of. a caustic base and air and a heavy metalcontaining oxidation catalyst,

sisting of silver, cobalt, copper,.manganese-and lead,

under elevated pressure, the. l-halogeno substituent being selected from the group consisting. of chlorine and broe mine.

10. A process for the production of tere'phthalicacid which comprises heating at temperatures from-about 265 to about 270 C. 1-chloromethyl-4-ethyl benzenein aque,-- ous suspension in the presence. .of a caustic base and: air and a heavy metal containing oxidation catalyst, wherein the heavy metal is selected from the group consisting of silver, cobalt, copper, manganese and lead,-i under elevated pressure.

11. A processv for the production of phthalic acid which comprises heating at temperatures. from about 150 to" about 250 C. l-chloromethyl-Z-methyl benzene in aqueous suspension in the'presence of a caustic 'base andair ing: about 7 hours, acidifying the reaction mixture and separatingthe terephthalic acid.

13..A:process.for the production of terephthalic'acid' which -;comprises, heating at. temperatures from about 265 tog 27 0 C. ,l-chloromethyl- 4-ethyl benzene-in aqueous. suspension in the presence of caustic sodaiandair and lead oxideand lead peroxide andga:pressurexofiaboutfi References Cited in the file of this patent UNITED STATES PATENTS Loder June 10, 1941 Henke et a1 Mar. 17, 1942 Gresham Aug. 16, 1949 Darragh et a1. Aug. 14, 1951 FOREIGN PATENTS Netherlands Aug. 15, 1949 Belgium Mar. 31, 1950 Great Britain May 24, 1949 Great Britain Oct. 18, 1950 

1. A PROCESS FOR THE PRODUCTION OF AROMATIC DICARBOXYLIC ACIDS WHICH COMPRISES HEATING AN AQUEOUE SUSPENSION OF A MONO-HALOGENOMETHYL MONO-LOWER ALKYL BENZENE, SAID LOWER ALKYL SUBSTITUENT CONTAINING AT LEAST ONE HYDROGEN SUBSTITUENT ON THE BENZENE-MOIETY-LINKING CARBON ATOM AND THE HALOGENO SUBSTITUENT BEING SELECTED FROM THE GROUP CONSISTING OF CHLORINE AND BROMINE, IN THE PRESENCE OF A CAUSTIC BASE AND OXYGEN AND A HEAVY METAL CONTAINTIN OXIDATION CATALYST, WHEREIN THE HEAVY METAL IS SELECTED FROM THE GROUP CONSISTING OF SILVER, COBALT, COPPER, AMNGANESE AND LEAD, AT TEMPERATURE RANGING FROM ABOUT 100*C. TO ABOUT 270*C. 